Fuel control racks that have become sticky or jammed may cause governing difficulties. If the control rack of a fuel system is not functioning properly, the engine speed may increase as the load is removed, the engine may hunt continuously, or it may hunt only when the load is changed. A sticky or jammed control rack may prevent the engine from responding to changes in throttle setting and may even prevent it from stopping. Any such condition could be serious in an emergency situation. Your job is to make every effort possible to prevent such conditions from occurring.

You can check for a sticky rack by stopping the engine, disconnecting the linkage to the governor, and then attempting to move the rack by hand. There should

Figure 3-41.Possible causes of insufficient power in an engine.

be no apparent resistance to the motion of the rack if the return springs and linkage are disconnected. A stuck control rack may be caused by the plungers sticking in the pump barrel; dirt in the rack mechanism; damage to the rack, sleeve, or gear; or improper assembly of the injector pump.

If the rack sticks or jams, you must determine the cause and replace any damaged parts. If sticking is due to dirt, thoroughly clean all the parts to correct the trouble. You can avoid errors in assembly by carefully studying the assembly drawings and instructions.

Leakage of Fuel Oil

Leakage of fuel oil from the injectors may cause an engine to continue to operate when you attempt to shut it down. Regardless of the type of fuel system, the results of internal leakage from injection equipment are, in general, somewhat the same. Injector leakage will cause unsatisfactory engine operation because of the excessive amount of fuel entering the cylinder. Leakage may also cause detonation, crankcase dilution, smoky exhaust, loss of power, and excessive carbon formation on the spray tips of nozzles and other surfaces of the combustion chamber.